This allows making the STATIC_ROOT read-only

Requires django-sass-processor 1.0

Resolve "[DOM] Found 2 elements with non-unique id #language-select"

Closes #418

See merge request !558

Resolve "404 pages broken due to django-menu-generator-ng"

Closes #411

See merge request !557

[Docker] Do not generate a secret key on startup

See merge request !556

This would require www-data to be able to write the secret key now.
That would not be an issue in general, but requires awkward changes
with no real use. Users are supposed to configure a secret key
themselves.

Update dependency calendarweek to ^0.5.0

See merge request !555

Merge branch '413-docker-allow-using-core-image-as-base-image-for-app-distribution-images' into 'master'

Resolve "[Docker] Allow using core image as base image for app/distribution images"

Closes #413

See merge request !550

Resolve "style.scss uses deprecated SCSS"

Closes #410

See merge request !551

Resolve "Can't connect to Redis with default configuration"

Closes #414

See merge request !553

Update dependency celery-progress to ^0.1.0

See merge request !546

Resolve "[Docker] Do not run as root"

Closes #409

See merge request !544

Update dependency django-haystack to v3.0

See merge request !548

Update dependency django-colorfield to ^0.4.0

See merge request !547

Run poetry update

See merge request !545

Previously, we relied on either explicit configuration to place the
file in a writable location, or the webserver being able to write to
the source tree.

With a (probably even replicated) setup where nothing runs as root,
and al lstorages are thus read-only except for the media storage, we
need to put the maintenance file there.